Magnetoresistive device and magnetoresistive head

ABSTRACT

A magnetoresistive device of the present invention includes: a soft magnetic layer; a hard magnetic layer; a non-magnetic layer formed between the soft magnetic layer and the hard magnetic layer; and an interface magnetic layer, provided at an interface between the soft magnetic layer and the non-magnetic layer, for enhancing magnetic scattering, wherein the soft magnetic layer includes an amorphous structure.

This application is a divisional of prior application Ser. No.08/802,711, filed Feb. 19, 1997 now U.S. Pat. No. 5,909,345.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetoresistive device in which alarge change in magnetoresistance is caused in a low magnetic field, andalso relates to a magnetoresistive head which is configured using such amagnetoresistive device and is suitable for high-density magneticrecording and reproducing operations.

2. Description of the Related Art

A magnetoresistive sensor (hereinafter, simply referred to as an "MRsensor") and a magnetoresistive head (hereinafter, simply referred to asan "MR head") using a magnetoresistive device (hereinafter, simplyreferred to as an "MR device) have been under development. The term "amagnetoresistive device" indicates a device which varies an electricresistance depending on the magnetic field externally applied. Thecharacteristic of the MR device is generally represented by a ratio ofchange of magnetoresistance (hereinafter abbreviated as an MR ratio).The MR ratio is defined by the following equation:

    MR ratio(%)=(R(maximum)-R(minimum))/R(minimum)×100

where R(maximum) and R(minimum) denote the maximum value and the minimumvalue of the resistance of the MR device when a magnetic field isapplied to the MR device.

Conventionally, a permalloy made of Ni₀.8 Fe₀.2 or an alloy layer madeof Ni₀.8 Co₀.2 is mainly used as the magnetic body. In the cases wheresuch magnetoresistive materials are used, the MR ratio is about 2.5%. Inorder to develop an MR device having higher sensitivity, an MR devicehaving a higher MR ratio is required. It was recently found that [Fe/Cr]and [Co/Ru] artificial multilayers in which antiferromagnetic couplingis attained via a metal non-magnetic thin layer made of a material suchas Cr and Ru exhibit a giant magnetoresistance (GMR) effect in aferromagnetic field (1 to 10 kilooersteds (kOe)) (Physical Review LetterVol. 61, p. 2472, 1988; and Physical Review Letter Vol. 64, p. 2304,1990). However, since these artificial multilayers require a magneticfield of several to several tens of kOe in order to attain a large MRchange, such artificial multilayers cannot be practically applied to amagnetic head and the like.

In addition, it was also found that an [Ni--Fe/Cu/Co] artificialmultilayer using magnetic thin layers made of Ni--Fe and Co havingdifferent coercive forces in which they are separated by a metalnon-magnetic thin layer made of Cu and which are not magneticallycoupled exhibits a giant magnetoresistance effect, and an artificialmultilayer which has an MR ratio of about 8% when a magnetic field ofabout 0.5 kOe is applied at room temperature has been hitherto obtained(see Journal of Physical Society of Japan, Vol. 59, p. 3061, 1990).However, in the case of using an MR material of such a type, a magneticfield of about 100 Oe is required for attaining a large MR change.Moreover, the MR asymmetrically varies from the negative magnetic fieldto the positive magnetic field, i.e., the MR exhibits poor linearity.Thus, such an artificial multilayer has characteristics which are notsuitable for practical use.

Moreover, it was also found that [Ni--Fe--Co/Cu/Co] and [Ni--Fe--Co/Cu]artificial multilayers using magnetic thin layers made of Ni--Fe--Co andCo in which RKKY-type antiferromagnetic coupling is attained via Cuexhibit a giant magnetoresistance effect, and an artificial multilayerwhich has an MR ratio of about 15% when a magnetic field of about 0.5kOe is applied at room temperature has been hitherto obtained (seeTechnical Report by THE INSTITUTE OF ELECTRONICS, INFORMATION ANDCOMMUNICATION ENGINEERS of Japan, MR91-9). However, in the case of usingan MR material of such a type, the magnetoresistance variessubstantially linearly from zero to the positive magnetic field andcharacteristics which are sufficiently suitable for the application toan MR sensor are obtained. Nevertheless, in order to obtain a large MRchange, a magnetic field of about 50 Oe is also required. Thus, such acharacteristic of the film is not appropriate for the application to anMR magnetic head which is required to be operated at most at 20 Oe andpreferably less.

As a film which can be operated even when a very weak magnetic field isapplied, a spin-valve type film in which Fe--Mn as an antiferromagneticmaterial is attached to Ni--Fe/Cu/Ni--Fe has been proposed (see Journalof Magnetism and Magnetic Materials 93, p. 101, 1991). The operatingmagnetic field of an MR material of this type is actually weak, and agood linearity is observed. However, the MR ratio thereof is as small asabout 2%, and the Fe--Mn layer has a poor corrosion resistance and a lowNeel temperature, so that the device characteristics disadvantageouslyexhibit great temperature dependence.

Furthermore, a spin-valve film having a structure of Ni--Fe/Cu/Co--Pt orthe like including a hard magnetic material such as Co--Pt instead of anantiferromagnetic material has also been suggested. In such a case, aparallel alignment of the magnetizations and an antiparallel alignmentof the magnetizations are caused by rotating the magnetization directionof a soft magnetic layer at a coercive force equal to or less than thatof a hard magnetic layer. However, even when such a structure isemployed, it is still difficult to improve the soft magneticcharacteristics of a soft magnetic layer. Thus, this structure has notbeen used practically, either.

In conventional magnetoresistive devices utilizing a giantmagnetoresistance effect, a crystalline Ni--Fe alloy or Ni--Fe--Co alloyis used for a soft magnetic layer. Thus, such magnetoresistive devicescannot totally eliminate magnetocrystalline anisotropy. Consequently, insuch conventional magnetoresistive devices, the soft magneticcharacteristics thereof are still poor and the operating magnetic fieldthereof cannot be strong.

On the other hand, it was recently reported that a magnetoresistanceeffect of about 5.4% is attainable even in a spin-valve film having astructure of Co--Fe--B/Cu/Co including a soft magnetic layer made of aCo--Fe--B amorphous alloy (see Japanese Journal of Applied Physics, Vol.34, pp. L112-L114, 1995). Since an amorphous alloy layer used as a softmagnetic layer exhibits more satisfactory soft magnetic characteristicsas compared with those of a conventional crystalline Ni--Fe alloy layeror Ni--Fe--Co alloy layer, a magnetoresistive device having highermagnetic field sensitivity can be fabricated. However, in the spin-valvefilm including the Co--Fe--B/Cu/Co structure, it was difficult tosimultaneously fulfill the incompatible purposes of obtaining asufficiently large MR ratio and a sufficiently high magnetic fieldsensitivity.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a magnetoresistivedevice includes: a soft magnetic layer; at least one hard magneticlayer; at least one non-magnetic layer formed between the soft magneticlayer and the at least one hard magnetic layer; and an interfacemagnetic layer, provided at an interface between the soft magnetic layerand the at least one non-magnetic layer, for enhancing magneticscattering, wherein the soft magnetic layer includes an amorphousstructure.

In one embodiment of the invention, the at least one hard magnetic layeris a pair of hard magnetic layers respectively arranged on both sides ofthe soft magnetic layer, and wherein the at least one non-magnetic layeris a pair of non-magnetic layers formed between the soft magnetic layerand the pair of hard magnetic layers.

Preferably, the hard magnetic layer has a ratio of remanentmagnetization to saturation magnetization is about 0.7 or more.

In another embodiment of the invention, the hard magnetic layer ispartially or entirely formed of oxide. The hard magnetic layer may beformed of an oxide of Co or an oxide of Fe.

In still another embodiment of the invention, the hard magnetic layercontains Co_(x) Fe_(1-x) as a main component, where x is in a range ofabout 0.3 to about 0.7.

In still another embodiment of the invention, the magnetoresistivedevice further includes an oxide layer formed on a side of the hardmagnetic layer opposite to a side on which the non-magnetic layer isformed. The oxide layer may be formed of an oxide of Ni.

In still another embodiment of the invention, the magnetoresistivedevice further includes an oxide magnetic layer formed on a side of thehard magnetic layer opposite to a side on which the non-magnetic layeris formed. The oxide magnetic layer may be formed of an oxide of Co oran oxide of Fe.

In still another embodiment of the invention, the magnetoresistivedevice further includes a further interface magnetic layer provided atan interface between the hard magnetic layer and the non-magnetic layer.Preferably, the further interface magnetic layer mainly contains Co orCo--Fe alloy and has a thickness of about 2 nm or less.

According to another aspect of the present invention, a magnetoresistivedevice includes: at least one metal antiferromagnetic layer; at leastone magnetic layer which is magnetically coupled with the at least onemetal antiferromagnetic layer; a soft magnetic layer; at least onenon-magnetic layer formed between the at least one magnetic layer andthe soft magnetic layer; and an interface magnetic layer, provided at aninterface between the soft magnetic layer and the at least onenon-magnetic layer, for enhancing magnetic scattering, wherein the softmagnetic layer includes an amorphous structure.

In one embodiment of the invention, the at least one metalantiferromagnetic layer is a pair of metal antiferromagnetic layersrespectively arranged on both sides of the soft magnetic layer, andwherein the at least one magnetic layer magnetically coupled with the atleast one metal antiferromagnetic layers is a pair of magnetic layersarranged on both sides of the soft magnetic layer.

According to still another aspect of the present invention, amagnetoresistive device includes: at least two soft magnetic layers; atleast one non-magnetic layer formed between the soft magnetic layers; atleast one metal antiferromagnetic layer formed on a side of one of thesoft magnetic layers opposite to a side on which the at least onenon-magnetic layer is formed; and an interface magnetic layer, providedat at least one interface between the at least one non-magnetic layerand the soft magnetic layers, for enhancing magnetic scattering, whereinat least one of the soft magnetic layers includes an amorphousstructure.

In one embodiment of the invention, the at least two soft layers arethree soft layers; the at least one non-magnetic layer is a pair ofnon-magnetic layers which are interposed between adjacent two of thethree soft layers, respectively; and the at least one metalantiferromagnetic layer is a pair of metal antiferromagnetic layersarranged to sandwich the three soft magnetic layers and the pair ofnon-magnetic layers therebetween.

In another embodiment of the invention, the magnetoresistive devicefurther includes a crystalline magnetic layer formed between the metalantiferromagnetic layer and the soft magnetic layer. The crystallinemagnetic layer may be formed of Ni--Fe--Co alloy.

The metal antiferromagnetic layer may be formed of M--Mn alloy, where Mis selected one of Ir, Pt, Pd and Ni. Preferably, the metalantiferromagnetic layer is formed of Ir--Mn alloy. Alternatively, themetal antiferromagnetic layer may be formed of Fe--Ir alloy.

In each of the above-described magnetoresistive devices, the interfacemagnetic layer may mainly contain Co or Co--Fe alloy, and have athickness of about 2 nm or less.

In each of the above-described magnetoresistive devices, thenon-magnetic layer may include a non-magnetic layer of a differentmaterial inserted therein. Preferably, the non-magnetic layer of thedifferent material has a thickness of about 1 nm or less.

In each of the above-described magnetoresistive devices, the softmagnetic layer may mainly contain Co--Mn--B alloy. Alternatively, thesoft magnetic layer may mainly contain Co--Nb--Zr alloy. Alternatively,the soft magnetic layer may mainly contain Co--Nb--B alloy.

In each of the above-described magnetoresistive devices, magnetizationeasy axis of the hard magnetic layer, the magnetic layer which ismagnetically coupled with the metal antiferromagnetic layer, or themagnetic layer which is in contact with the metal antiferromagneticlayer substantially coincides with a direction of a magnetic field to bedetected, and the magnetoresistive device has a thickness of about 20 nmor less.

According to still another aspect of the invention, a magnetoresistivehead includes any one of the above-described magnetoresistive devicesand a lead portion.

Thus, the invention described herein makes possible the advantage ofproviding a magnetoresistive device which can simultaneously improveboth an MR ratio and a magnetic field sensitivity and a magnetoresistivehead using such a magnetoresistive device.

This and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing an embodiment ofthe magnetoresistive device of the present invention.

FIG. 2 is a cross-sectional view schematically showing anotherembodiment of the magnetoresistive device of the present invention.

FIG. 3 is a cross-sectional view schematically showing still anotherembodiment of the magneto-resistive device of the present invention.

FIG. 4 is a cross-sectional view schematically showing still anotherembodiment of the magneto-resistive device of the present invention.

FIG. 5 is a cross-sectional view schematically showing still anotherembodiment of the magnetoresistive device of the present invention.

FIGS. 6A, 6B and 6C are cross-sectional views schematically showingstill other embodiments of the magnetoresistive device of the presentinvention.

FIG. 7 is a cross-sectional view schematically showing still anotherembodiment of the magneto-resistive device of the present invention.

FIG. 8 is a cross-sectional view schematically showing still anotherembodiment of the magneto-resistive device of the present invention.

FIG. 9 is a cross-sectional view showing an exemplary magnetoresistivehead of the present invention.

FIG. 10 is a graph representing the dependence of an MR ratio upon thethickness of a Co layer as an interface magnetic layer in an exemplarymagnetoresistive device having the structure shown in FIG. 1.

FIG. 11 is a graph representing the dependence of an MR sensitivityΔMR/ΔH upon the thickness of the Co layer as the interface magneticlayer in the exemplary magnetoresistive device having the structureshown in FIG. 1.

FIG. 12 is a diagram illustrating the definition of the MR sensitivityΔMR/ΔH.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the MR device and the MR head according to the presentinvention will be described with reference to the accompanying drawings.

(Embodiment 1)

FIG. 1 schematically shows the cross section of an exemplary embodimentof the MR device of the present invention. In the MR device shown inFIG. 1, an amorphous alloy layer 1 as a soft magnetic layer, a hardmagnetic layer 4 and a non-magnetic layer 3 sandwiched therebetween. Thenon-magnetic layer 3 is provided for weakening magnetic coupling betweenthe hard magnetic layer 4 and the amorphous alloy layer 1. The MR deviceof the present embodiment further includes another magnetic layer 2inserted into the interface between the non-magnetic layer 3 and theamorphous alloy layer 1. The magnetic layer 2 is provided for enhancingspin-dependent scattering of the conduction electrons occurring at theinterface of the layers 1 and 3. The magnetization of the amorphousalloy layer 1 as the soft magnetic layer can be rotated (inverted) byapplication of a relatively weak magnetic field, whereas themagnetization of the hard magnetic layer 4 is not rotated. Thus, when amagnetic field to be detected as a signal is applied to the MR device,only the magnetization of the amorphous alloy layer 1 is rotated inaccordance with the applied magnetic field, resulting in change in anglebetween magnetization directions of the amorphous alloy layer 1 and thehard magnetic layer 4. As a result, an electric resistance of the MRdevice is changed.

In this specification, a magnetic layer having a coercive force of 100Oe or more is referred to as "a hard magnetic layer", and a magneticlayer having a coercive force of 20 Oe or less is referred to as "a softmagnetic layer". In addition, a magnetic layer having a coercive forcewhich is larger than that of the soft magnetic layer and is smaller thanthat of the hard magnetic layer is referred to as "a semi-hard magneticlayer".

The operation principle of the MR device of the present invention willbe described below. In the case where the hard magnetic layer 4 isunidirectionally magnetized by a ferromagnetic field, when a weak signalmagnetic field having a direction opposite to the direction in which thehard magnetic layer 4 is magnetized is applied to the MR device, themagnetization of the hard magnetic layer 4 is not rotated, but themagnetization of the amorphous alloy layer 1 as the soft magnetic layeris rotated to the direction of the magnetic field. As a result, themagnetization direction of the hard magnetic layer 4 is anti-parallel tothe magnetization direction of the amorphous alloy layer 1. When themagnetization direction of the hard magnetic layer is anti-parallel tothat of the amorphous alloy layer 1, the conduction electrons in the MRdevice is subjected to magnetic scattering, mainly at interfaces betweenthe hard magnetic layer 4 and the non-magnetic layer 3 and between thenon-magnetic layer 3 and the interface magnetic layer 2. As a result,the electric resistance of the MR device increases.

On the other hand, when a weak magnetic field having the same directionas the direction in which the hard magnetic layer 4 is magnetized isapplied to the MR device, the magnetization direction of the hardmagnetic layer 4 is parallel to that of the amorphous alloy layer 1. Asa result, the above-mentioned magnetic scattering is reduced so that theelectric resistance of the MR device is reduced. On the basis of theabove-mentioned principle, the MR device varies its electric resistancedepending on the change in the signal magnetic field.

In a conventional spin-valve type MR device, since a crystalline Ni--Fealloy or Ni--Fe--Co alloy layer is used as a soft magnetic layer, themagnetic field required for inverting the magnetization of the softmagnetic layer, i.e., the operating magnetic field cannot besufficiently weakened. However, according to the present invention, anamorphous alloy layer is used as a soft magnetic layer. Since themagnetocrystalline anisotropy of an amorphous alloy layer is smallerthan that of a crystalline alloy layer, the coercive force thereof canbe sufficiently weakened, thereby weakening the operating magneticfield. In the case of using a layer which is perfectly in an amorphousstate, the magnetocrystalline anisotropy thereof is zero, and thus, thecoercive force thereof can be greatly weakened. In this specification, aterm "an amorphous layer" indicates a layer including an amorphousstructure, but is not limited to a layer which is perfectly in anamorphous state. In view of the application to a magnetic head or thelike, the thickness of an amorphous alloy layer of the present inventionis preferably 10 nm or less, more preferably 5 nm or less. However, itis difficult to confirm whether or not such a thin layer is totallyamorphous by an X-ray diffraction or the like. Thus, if a layer as thickas about 100 nm is fabricated, then the amorphous structure of the layercan be easily confirmed.

The amorphous alloy materials usable for the amorphous alloy layer 1include: Co--M--B (where M=Mn, Fe) materials including boron (B) byabout 15-30 atomic percent; Co--T materials (where T=Nb, Ta, Zr, Hf)including non-magnetic transition metals T by about 6 to 25 atomicpercent; and Co(--M)--T--B materials which are intermediate between theabove-cited two types of materials and include B, T and M by about 2-15atomic percent, 2-20 atomic percent and about 5 atomic percent,respectively (in this case, M is added for adjusting themagnetostriction). The materials mainly composed of Co--Mn--B areparticularly suitable for attaining a large MR ratio. The materialsmainly composed of Co--Nb--Zr are particularly suitable with respect tocorrosion resistance and soft magnetic characteristics. And thematerials mainly composed of Co--Nb--B exhibit intermediate balancedcharacteristics between the Co--Mn--B materials and the Co--Nb--Zrmaterials.

The Co--Mn--B materials are preferably composed so as to have acomposition ratio where the magnetostriction thereof becomessubstantially zero (absolute value of the magnetostriction becomes 10⁻⁵or less). Thus, the atomic composition ratio of the Co--Mn--B materialsis preferably represented by:

    Co.sub.1-x-y Mn.sub.x B.sub.y

(where 0.05≦x≦0.08 and 0.15≦y≦0.3).

In the case of the Co--Fe--B materials, the atomic composition ratiothereof is preferably represented by:

    Co.sub.1-x'-y' Fe.sub.x' B.sub.y'

(where 0.05≦x'≦0.06 and 0.15≦y'0.3).

In the case of the Co--Nb--Zr materials, the atomic composition ratiothereof is preferably represented by:

    Co.sub.1-"-y" Nb.sub.x" Zr.sub.y"

(where 0.06≦x"≦0.20 and 0.03≦y"≦0.10).

And in the case of the Co--Nb--B materials, the atomic composition ratiothereof is preferably represented by:

    Co.sub.1-u-v Nb.sub.u B.sub.v

(where 0.02≦u≦0.15 and 0.02≦v≦0.20). However, the magnetostriction ofthe Co--Nb--B materials is slightly lower than zero. Thus, in order toadjust the magnetostriction thereof to be zero, Fe or Mn is preferablyadded thereto by the atomic composition ratio of about 1 to 5 percent.

In the foregoing description, the compositions of alloys, which canprovide Co--Mn--B, Co--Fe--B, Co--Nb--Zr and Co--Nb--B alloys which areperfectly in an amorphous state, are described. However, the softmagnetic layer of the present invention is not always required to beperfectly amorphous. Alternatively, the soft magnetic layer may have asmall amount of crystalline material or may include a microcrystallinestructure. In this case, the MR ratio is certainly improved but the softmagnetic characteristics thereof tend to deteriorate to a certaindegree. A specific atomic composition ratio applicable to Co_(1-x-y)Mn_(x) B_(y) with a crystalline material mixed may be represented by:

    0.05≦x≦0.08 and 0.05≦y≦0.15

On the other hand, a specific atomic composition ratio applicable toCo_(1-x'-y') Fe_(x') B_(y') with a crystalline material mixed may berepresented by:

    0.05≦x'≦0.06 and 0.05≦y'≦0.15.

The hard magnetic layer 4 is preferably made of a ferromagnetic materialwhich exhibits a magnetization curve having a good square feature. Inthis specification, a "good square feature" is defined so that thesquare ratio S (=remanent magnetization/saturation magnetization) isabout 0.7 or more. It is more preferable that a ferromagnetic materialexhibiting the square ratio of about 0.85 or more is used as the hardmagnetic layer 4. If the square ratio of the hard magnetic layer 4 isunsatisfactory, then a perfectly parallel alignment of themagnetizations or a perfectly antiparallel alignment of themagnetizations state cannot be established between the hard magneticlayer 4 and a soft magnetic layer (the amorphous alloy layer 1 in the MRdevice of the present invention), resulting in poor linearity and smallMR ratio.

Materials mainly composed of Co (over 50 atomic %) is preferable forobtaining a large MR ratio. Among such materials, Co, Co--Fe alloys andCo--Pt alloys exhibit excellent characteristics as materials for thehard magnetic layer. Co and Co--Fe alloys are particularly preferable.More preferably, Co--Fe alloys having the following atomic compositionratio

    Co.sub.1-x Fe.sub.x

(where 0.3≦x≦0.7)

is used.

In the foregoing description, the hard magnetic layer 4 is assumed to becomposed of a single layer of metal or a single layer of metal alloy.Optionally, an oxide layer or an oxide magnetic layer may be furtherprovided on the side of the hard magnetic layer 4 opposite to thenon-magnetic layer 3. By additionally providing such an oxide layer oran oxide magnetic layer, it is relatively easy to sufficiently increasethe coercive force of the hard magnetic layer 4. In such a case, thesquare ratio of the hard magnetic layer 4 can be increased as a wholeand the MR ratio thereof can be further increased. Ni--O or the like maybe used as a material for the oxide layer and Co--O, Fe--O, Co--Fe--O orthe like may be used as a material for the oxide magnetic layer.

Alternatively, the hard magnetic layer 4 may be totally replaced by anoxide magnetic layer. In such a case, Co--O, Fe--O, Co--Fe--O or thelike may also be used as a material for the oxide magnetic layer.

The non-magnetic layer 3 is formed in order to weaken magnetic couplingbetween the hard magnetic layer 4 and the amorphous alloy layer 1 as thesoft magnetic layer. Thus, a material for the non-magnetic layer 3 andthe thickness thereof are selected considering this purpose.Specifically, Cu, Ag, Au, Ru or the like may be used as a material forthe non-magnetic layer 3 between the hard magnetic layer 4 and a softmagnetic layer (the amorphous alloy layer 1). Among these materials, Cuis most suitably used. In order to weaken the interaction between thetwo magnetic layers 4 and 1, the thickness of the non-magnetic layer 3is required to be at least about 1.5 nm or more, desirably about 1.8 nmor more. On the other hand, if the non-magnetic layer 3 becomes toothick, then the MR ratio thereof is adversely decreased. Thus, thethickness of the non-magnetic layer 3 should be about 10 nm or less,desirably about 3 nm or less.

In addition, it is also effective to insert another non-magnetic layerwhich is formed of a different material from that of the non-magneticlayer 3 into the non-magnetic layer 3 for reducing the magnetic couplingbetween the hard magnetic layer 4 and the soft magnetic layer (theamorphous alloy layer 1). In other words, the non-magnetic layer 3 canbe composed of a plurality of non-magnetic layers formed of differentmaterials. For example, instead of forming a single-layer non-magneticlayer of Cu, the non-magnetic layer may have a multilayer structure suchas Cu/Ag/Cu, Cu/Ag and Ag/Cu/Ag. The non-magnetic layer to be insertedis preferably made of Ag, Au or the like. In this case, the thickness ofthe multilayer non-magnetic layer is desirably approximately equal tothat of the single-layer non-magnetic layer. The thickness of anon-magnetic layer to be inserted into the non-magnetic layer 3 is atmost about 1 nm, desirably about 0.4 nm or less.

Next, the interface magnetic layer 2 inserted into the interface betweenthe non-magnetic layer 3 and the amorphous alloy layer 1 as the softmagnetic layer will be described below. As described above, the insertedinterface magnetic layer 2 enhances a spin-dependent scattering of theconduction electrons, thereby increasing the MR ratio. In addition, whenthe thickness of the interface magnetic layer 2 is set to be an adequatethickness, an MR sensitivity (ΔMR/ΔH) is also improved. In this case,ΔMR/ΔH is defined as a change in MR ratio with respect to a change inapplied magnetic field from the zero magnetic field, as shown in FIG.12. The interface magnetic layer 2 improves the MR sensitivity ΔMR/ΔH aswell as the MR ratio, presumably because the interface magnetic layer 2increases the magnetic scattering in the interface between a magneticlayer and a non-magnetic layer. In addition, an interface magnetic layer2 having a small thickness presumably has an effect of improving thesoft magnetic characteristics of the amorphous alloy layer 1. However,if the interface magnetic layer 2 is too thick, then the soft magneticcharacteristics of the soft magnetic layer are degraded as a whole andthe magnetic field sensitivity of the MR ratio is deteriorated. Thus, inorder to avoid the deterioration of the soft magnetic characteristics ofthe amorphous alloy layer 1, the thickness of the interface magneticlayer 2 is preferably set to about 2 nm or less, more preferably about1.8 nm or less. On the other hand, in order to make the interfacemagnetic layer 2 function effectively, the thickness thereof is requiredto be at least 0.2 nm, desirably 0.8 nm or more.

A material for the interface magnetic layer 2 is selected so that itenhances the spin-dependent scattering of the conduction electrons, andthat the combination of the interface magnetic layer 2 and the softmagnetic layer (the amorphous alloy layer) 1 serves as a soft magneticlayer. Specifically, materials mainly composed of Co (over 50 atomic %)is suitable for the material of the interface magnetic layer 2 of thepresent invention, more preferably Co or a Co--rich Co--Fe alloy.

In the foregoing description, an interface magnetic layer is assumed tobe inserted between the non-magnetic layer 3 and. the amorphous alloylayer 1. Optionally, another interface magnetic layer may be insertedbetween the non-magnetic layer 3 and the hard magnetic layer 4. In thiscase, magnetic scattering within the MR device is enhanced, therebygreatly increasing the MR ratio. As well as the interface magnetic layer2 interposed between the non-magnetic layer 3 and the amorphous alloylayer 1, a material for the additional interface magnetic layer to beinserted between the non-magnetic layer 3 and the hard magnetic layer 4and the thickness thereof are selected so as to deteriorate the magneticcharacteristics (e.g., coercive force and square ratio of the magneticcurve) of the hard magnetic layer 4. Specifically, if the thickness ofthe additional interface magnetic layer is about 2 nm or less, the MRratio can be increased substantially without varying the characteristicsof the hard magnetic layer 4. In particular, in the case ofincorporating the MR device of the present embodiment in an magnetichead or the like, it is preferable to set the thickness of theadditional interface magnetic layer between the hard magnetic layer 4and the non-magnetic layer 3 to be 1 nm or less.

The structure shown in FIG. 1 is a basic structure of the MR device ofthe present embodiment including a hard magnetic layer 4, a non-magneticlayer 3, an interface magnetic layer 2 and an amorphous alloy layer 1 indescending order. Alternatively, in order to further increase the MRratio, a structure shown in FIG. 2 including a hard magnetic layer 4, anon-magnetic layer 3, an interface magnetic layer 2, an amorphous alloylayer 1, an interface magnetic layer 2, a non-magnetic layer 3 and ahard magnetic layer 4 in descending order may also be used. A giantmagnetoresistance (GMR) effect has conventionally been explained asresulting from spin-dependent scattering of the conduction electronsoccurring at the interface between a magnetic layer and a non-magneticlayer (for example, Physical Review B, vol. 42, pp. 8110-8120). Thus, ifthe number of layers to be stacked is so increased that the totalthickness of the multilayer structure is approximately comparable to themean free path of the electrons, then the magnetic scattering isenhanced, thereby increasing the MR ratio.

The conditions, such as the materials and the thicknesses for therespective layers shown in FIG. 2 are totally the same as thosedescribed for the layers shown in FIG. 1.

(Embodiment 2)

In Embodiment 1, the present invention has been applied to a spin-valvetype MR device including a hard magnetic layer. Alternatively, thepresent invention is effectively applicable to a spin-valve type MRdevice including a combination of a magnetic layer 5, which is arrangedin contact with the non-magnetic layer 3, and a metal antiferromagneticlayer 6 having a function of unidirectionally magnetizing the magneticlayer 5 by directly exerting an exchange coupling interaction on themagnetic layer 5, in place of a hard magnetic layer.

FIG. 3 shows a cross section of an MR device of the present embodimentin which an amorphous alloy layer 1 as a soft magnetic layer is providedon one side of a non-magnetic layer 3 and a magnetic layer 5 is providedon the other side of the non-magnetic layer 3. A metal antiferromagneticlayer 6 is provided on the side of the magnetic layer 5 which isopposite to the side on which the non-magnetic layer 3 is located.Furthermore, an interface magnetic layer 2 is provided between theamorphous alloy layer 1 and the non-magnetic layer 3, as in Embodiment1.

Fe--Mn, Ni--Mn, Pd--mn, Pt--Mn, Ir--Mn, Fe--Ir and the like may be usedas the materials for the metal antiferromagnetic layer 6. Among thesematerials, Fe--Mn has been used most frequently in a conventionalspin-valve film. However, this material causes some problems inpractical use in view of the corrosion resistance and the like of thematerial. In respect of the corrosion resistance, materials such asIr--Mn are particularly preferable. The appropriate atomic compositionratio of an Ir_(z) Mn_(1-z) is: 0.1≦z≦0.5. If oxides such as Ni--O,Co--O and Ni--O/Co--O are not appropriate for the materials for theantiferromagnetic layer 6, then the thickness of the antiferromagneticlayer 6 is required to be large for attaining excellent magneticcharacteristics. However, in order to shorten the recording wavelengthof a magneto-resistance effect device for preparing for the superhigh-density recording to be developed in the near future, the totalthickness of an MR device is required to be reduced. Thus, such oxidesare not suitable as the materials for the antiferromagnetic layer 6.

Co, Ni--Fe, Ni--Fe--Co and the like are desirable as the materials forthe magnetic layer 5. The conditions, such as the materials and thethicknesses, for the other layers shown in FIG. 3 (i.e., the amorphousalloy layer 1, the interface magnetic layer 2 and the non-magnetic layer3) are totally the same as those described for the corresponding layersshown in FIG. 1.

Furthermore, the MR device of the present embodiment may have astructure including a metal antiferromagnetic layer 6, a magnetic layer5, a non-magnetic layer 3, an interface magnetic layer 2, an amorphousalloy layer 1, an interface magnetic layer 2, a non-magnetic layer 3, amagnetic layer 5 and a metal antiferromagnetic layer 6 in descendingorder, as shown in FIG. 4. In this case, since the number of interfacesbetween magnetic layers and non-magnetic layers is increased, the MRratio is also increased.

The conditions for the respective layers shown in FIG. 4 are the same asthose described for the layers shown in FIG. 3.

(Embodiment 3)

The MR device according to the third embodiment of the present inventionis illustrated in FIG. 5. In the present embodiment, a pair of amorphousalloy layers 1 are formed as soft magnetic layers sandwiching anon-magnetic layer 3 therebetween, and a metal antiferromagnetic layer 6is further formed in contact with the upper one of the pair of amorphousalloy layers 1.

Referring to FIG. 5, the amorphous alloy layer 1 in contact with themetal antiferromagnetic layer 6 is generally called a "pinned layer".The magnetization direction of the amorphous alloy layer 1 as the pinnedlayer is fixed to be unidirectional by the exchange coupling interactionwhich has been directly applied from the metal antiferromagnetic layer6. On the other hand, the amorphous alloy layer 1 not in contact withthe metal antiferromagnetic layer 6 is called a "free layer". Themagnetization direction of the amorphous alloy layer 1 as the free layercan be freely rotated. There is a difference in magnetoresistance of theMR device between when the magnetization directions of the pinned layerand the free layers are parallel and when the magnetization directionsare antiparallel. The operation of such an MR device utilizes a changein the magnetoresistance generated by inverting the magnetizationdirection of the free layer in accordance with the applied magneticfield while fixing the magnetization direction of the pinned layer.

The conditions (materials, thicknesses and the like) for the respectivelayers shown in FIG. 5, i.e, the amorphous alloy layers 1, thenon-magnetic layer 3 and the metal antiferromagnetic layer 6 are thesame as those described for the layers shown in FIG. 3.

FIG. 5 shows a case where the metal antiferromagnetic layer 6 is incontact with one of the amorphous alloy layers 1. Optionally, acrystalline magnetic layer may be inserted between the metalantiferromagnetic layer 6 and the amorphous alloy layer 1. Since themetal antiferromagnetic layer 6 is generally crystalline, if the softmagnetic layer (i.e., the upper amorphous alloy layer 1) functioning asthe pinned layer is also crystalline, then the biasing magnetic fieldcausing an exchange coupling interaction which has been applied from themetal antiferromagnetic layer 6 is increased, so that a force fixing themagnetization direction is strengthened. Thus, if a crystalline magneticlayer is inserted between the metal antiferromagnetic layer 6 and theamorphous alloy layer 1, then the magnetization direction of the pinnedlayer can be further stabilized. Ni--Fe--Co alloys, Ni--Fe alloys, Coand the like are desirable as the materials for the crystalline magneticlayer. If the thickness of the crystalline magnetic layer is about 0.4nm or less, then satisfactory effects cannot be attained. Thus, thethickness of the crystalline magnetic layer is preferably about 1 nm ormore. Nevertheless, if the thickness is too large, then the MR ratio isadversely decreased. Consequently, the thickness of the crystallinemagnetic layer is preferably about 5 nm or less, more preferably about 2nm or less.

The structure shown in FIG. 5 is a basic structure of the MR device ofthe present embodiment including an amorphous alloy layer 1, anon-magnetic layer 3, another amorphous alloy layer 1 and a metalantiferromagnetic layer 6 in ascending order. Alternatively, in order tofurther increase the MR ratio, a structure shown in FIG. 7 including ametal antiferromagnetic layer 6, an amorphous alloy layer 1, anon-magnetic layer 3, an amorphous alloy layer 1, a non-magnetic layer3, an amorphous alloy layer 1, and a metal antiferromagnetic layer 6 indescending order may also be used. A giant magnetoresistance effect hasconventionally been explained as resulting from the spin-dependentscattering of the conduction electrons occurring at the interfacebetween a magnetic layer and a non-magnetic layer. Thus, if the numberof layers to be stacked is so increased that the total thickness of themultilayer structure is approximately comparable to the mean free pathof the electrons, then the MR ratio can be increased

The conditions for the respective layers shown in FIG. 7 are the same asthose described for the layers shown in FIG. 5.

(Embodiment 4)

Next, an MR device according to the fourth embodiment of the presentinvention will be described with reference to FIGS. 6A, 6B and 6C and 8.FIGS. 6A to 6C show exemplary cross sections of the MR device of thepresent embodiment, and FIG. 8 shows a cross section of an MR deviceaccording to a modification of the present embodiment. As shown in thesefigures, in the MR device of the present embodiment and themodification, an interface magnetic layer 2 is inserted into at leastone interface between a non-magnetic layer 3 and an amorphous alloylayer 1. In order to attain a sufficient effect, a pair of interfacemagnetic layers 2 are inserted on both sides of the non-magnetic layer 3as shown in FIG. 6A. However, even when only one interface magneticlayer 2 is inserted on either side of the non-magnetic layer 3 as shownin FIGS. 6B and 6C, effects can be still attained. The interfacemagnetic layer 2 increases not only the MR ratio but also the MRsensitivity (ΔMR/ΔH) shown in FIG. 12.

In Embodiments 1-4, each of the amorphous alloy layer 1 as the softmagnetic layer, the interface magnetic layer 2, the non-magnetic layer3, the hard magnetic layer 4, the magnetic layer 5, and the metalantiferromagnetic layer 6 may be formed by a sputtering method or anevaporation method. In either case, the MR device of the presentinvention can be fabricated. However, it should be noted that asputtering method is particularly suitable for fabricating an amorphousalloy layer 1. Various sputtering techniques including DC sputtering, RFsputtering and ion beam sputtering may be applicable. In any of thesetechniques, the magneto-resistance effect device of the presentinvention can be fabricated. On the other hand, in the case of using anevaporation method, a super high vacuum evaporation technique isparticularly preferable.

The MR devices described in Embodiments 1-4 are actually fabricated on asubstrate, such as a glass substrate. In fabrication of these MRdevices, layers constituting the MR devices are formed on the substrateeither in the order of lowermost layer to uppermost layer (for example,the amorphous alloy layer 1, the interface magnetic layer 2,non-magnetic layer 3 and the hard magnetic layer 4 in the MR device asshown in FIG. 1) or in the inverse order of the uppermost layer to thelower-most layer. Moreover, the MR devices as described in Embodiments1-4 may be formed directly on the substrate. Alternatively, anunderlying layer formed of, for example, Ta, Cr, Fe, Cu, Ag, Ru or thelike, may be formed on the substrate before fabricating the MR devices,and then the MR devices may be formed on the underlying layer.

An magnetoresistive head (MR head) can be formed by using theabove-described MR device of the present invention. An exemplarystructure of an MR head of a hard layer biasing type is shown in FIG. 9.As shown in FIG. 9, an MR device 7 is formed so as to be interposedbetween an upper insulating layer 9 and a lower insulating layer 12.Materials such as Al₂ O₃ and SiO₂ are usable for the insulating layers 9and 12. A pair of shields 8 and 13 are further formed on the outer sideof the upper insulating layer 9 and on the outer side of the lowerinsulating layer 12, respectively. A soft magnetic layer made of anNi--Fe alloy or the like is used as the shields 8 and 13.

In the MR head of the present invention, a pinned layer (a hard magneticlayer 4 or a magnetic layer in contact with a metal antiferromagneticlayer 6) of the MR device 7 is magnetized so that the magnetizationdirection coincides with a signal magnetic field to be detected (adirection perpendicular to the sheet surface in FIG. 9), and amagnetization easy axis of a free layer (i.e., a soft magnetic layer isadjusted to be perpendicular to the signal magnetic field). Hard biasingportions 11 is formed of a Co--Pt alloy or the like in order tostabilize the magnetization direction of the soft magnetic layer (i.e.,to uniaxially magnetize the soft magnetic layer) by applying a biasingmagnetic field. Thus, Barkhausen noise can be prevented from occurringwhen the magnetization direction of the soft magnetic layer is rotated.In FIG. 9, a hard magnetic layer is assumed to be used for applying thebiasing magnetic field. Alternatively, an antiferromagnetic materialsuch as Fe--Mn may also be used. The MR device 7 is electricallyinsulated from the shields 8 and 13 via the insulating layers 9 and 12.

The MR head is used only for reading a signal recorded on a recordingmedium and is of an inductive type which reads the signal utilizing aninduction. Thus, when the MR head is operated, a leakage magnetic fieldfrom the surface of the recording medium functions as a signal magneticfield. In the operation of the MR head having a structure shown in FIG.9, the signal magnetic field is applied in a direction parallel to themagnetization difficult axis of the free layer (the soft magnetic layer)of the MR device 7, thereby the magnetization direction of the softmagnetic layer is rotated. As a result, an angle between themagnetization direction of the pinned layer, which is fixed, and themagnetization direction of the free layer is changed, resulting inchange in electric resistance of the MR device 7. By supplying a currentthrough a lead portion 10, the electric resistance change can bedetected as an output voltage.

In order to realize a super high density for a hard disk drive in thenear future, the recording wavelength of the MR device 7 is required tobe shortened. Thus, the distance d between the shields 8 and 13 (i.e., ashield gap) is required to be reduced, which in turn requires reductionin thickness of the MR device portion 7 as is clear from FIG. 9. Thethickness of the MR device portion 7 is preferably at most about 20 nm.The MR device of the present invention is suitably formed as such athin-film device.

Hereinafter, the MR device and the MR head of the present invention willbe described by way of specific examples.

EXAMPLE 1

An MR device A0 having a structure shown in FIG. 1 was formed on asubstrate (for example, a glass substrate) by an RF magnetron sputteringapparatus using a ternary target Co₀.68 Mn₀.06 B.sub. 0.26. The specificstructure of the MR device A0 is as follows:

A0: Co₀.06 Mn₀.06 B₀.26 (2 nm)/Co (x nm)/Cu (2 nm)/Co (2 nm)

where the numerical values in parentheses indicate layer thicknesses andthe composition ratio of Co--Mn--B is represented by the compositionratio of the target.

For comparison, a comparative MR device A1 having a similar structureexcept for including Ni--Fe alloy layer as a soft magnetic layer inplace of a Co₀.68 Mn₀.06 B.sub. 0.26layer w as fabricated by a similarfabrication method.

A1: Ni₀.8 Fe₀.2 (2 nm)/Co (x nm)/Cu (2 nm)/Co (2 nm)

The characteristics of the MR devices A0 and A1 fabricated in such amanner were evaluated by a direct current four-terminal method byapplying an external magnetic field of about 500 Oe at room temperature.The evaluation results are shown in FIGS. 10 and 11. As seen from FIG.10, the MR device A0 of the present invention has a larger MR ratio thanthat of the comparative device A1. This is probably because a softmagnetic layer made of an Ni--Fe alloy has a coercive force which is notso much different from that of a hard magnetic layer 4. Thus, in aconventional structure, it is difficult to realize the antiparallelalignment of the magnetizations.

In addition, in the device A0, the Co layer 2 is inserted as theinterface magnetic layer into the interface between the non-magneticlayer 3 and the amorphous alloy layer 1. Thus, when the thickness of theCo layer 2 is small, the MR ratio and the value of the MR sensitivityΔMR/ΔH are increased as shown in FIGS. 10 and 11. The increase in MRratio and MR sensitivity ΔMR/ΔH presumably results from the improvementof the soft magnetic characteristics of the amorphous alloy layer causedby the insertion of the Co layer. Another cause for the increase in MRratio presumably lies in that the degree of the magnetic scattering ofconduction electrons is larger in the interface between the non-magneticlayer 3 and the Co layer 2 than in the interface between thenon-magnetic layer 3 and amorphous alloy layer 1. As shown in FIG. 10,the MR ratio is remarkably increased when the thickness of the Co layer2 is. equal to or larger than about 0.8 nm but the MR ratio is ratherdecreased when the thickness of the Co layer 2 is equal to or largerthan 2 nm. The reasons for the decrease in MR ratio are probably asfollows: when the Co layer 2 as the interface magnetic layer becomes toothick, the soft magnetic characteristics of the combination of theinterface magnetic layer and the amorphous alloy layer are degraded, sothat the antiparallel alignment of the magnetizations cannot beestablished easily.

When the MR device A0 (where the thickness (x) of the Co layer 2 isabout 1.5 nm) was reserved within a thermostatic oven at 50° C. under anatmospheric pressure for a month, an oxide layer having a thickness ofabout 0.5 nm was formed on the surface of the Co layer as the hardmagnetic layer, so that the MR ratio increased up to about 8%. On theother hand, substantially the same effects were attained in the casewhere an Ni--O layer or a Co--O layer having a thickness of about 0.5 nmwere formed on the Co layer as the hard magnetic layer by sputteringusing an Ni target or a Co target while mixing an O₂ gas (about 10%) asa sputtering gas into the Ar gas (instead of annealing the fabricateddevice in the above-described manner) after the MR device A0 had beenformed. In this example, an Ni--O layer or a Co--O layer is assumed tobe formed as an oxide layer. However, the present invention is alsoapplicable to the case of fabricating an Fe--O layer or an Fe--Co--Olayer in substantially the same way. The magnetic characteristics ofsuch oxide layers are variable depending upon the composition thereof(i.e., sometimes these oxide layers become antiferromagnetic layers andsometimes hard magnetic layers). However, in any case, by combining suchoxide layer with the metal magnetic layer, the increased coercive forceis obtained, and the magnetization direction of the hard magnetic layer4 is fixed, thereby increasing the MR ratio.

On the other hand, an MR device A2 having a similar structure except forincluding an oxide magnetic layer as the hard magnetic layer wasfabricated. The specific structure of the MR device A2 is as follows.

A2: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (1.5 nm)/Cu (2 nm)/Co--O (2 nm)

the MR ratio thereof became slightly lower (i.e., about 4.2%). However,in this device A2, since the coercive force of the Co--O layer was about100 Oe (i.e., about twice as strong as that of the Co layer), it can beseen that the device A2 has a stabler output with respect to an externallarge magnetic field applied accidentally.

Furthermore, in order to compensate for the disadvantages of the MRdevice A2, the following structure was modeled:

A3: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (1.5 nm)/Cu (2 nm)/Co (1.5 nm)/Co--O(2 nm)

The MR ratio of the MR device A3 was about 6.5% and the coercive forceof the hard magnetic layer 4 was as excellent as that of the device A2.The increase in MR ratio of the device A3 presumably results from theenhanced effect of the spin-dependent scattering of the conductionelectrons caused by the newly provided interface between Co and Cu.

In the MR devices A0, A2 and A3 of the present invention, a Co--Mn--Blayer is used as the amorphous alloy layer. However, the corrosionresistance of the Co--Mn--B layer and a Co--Fe--B layer is slightlydeteriorated under extremely bad conditions (e.g., in water or in salinewater). In order to eliminate such a disadvantage, a Co--Nb--Zr layermay be used. When an MR device A4 having the following structure wasmodeled in a similar manner to the MR device A3 except for using Co₀.85Nb₀.1 Zr₀.05 as a target,

A4: Co₀.85 Nb₀.1 Zr₀.05 (2 nm)/Co (1.5 nm)/Cu (2 nm)/Co (1.5 nm)/Co--O(2 nm)

the MR ratio thereof was about 5.5%.

In the foregoing description, a Co--O layer is assumed to be formed asan oxide layer. However, the present invention is effectively applicablein substantially the same way to the cases of forming an Fe--O layer andan Fe--Co--O layer.

Furthermore, in order to examine the characteristics of the non-magneticlayer, the following three types of devices A5, A6 and A7 werefabricated by replacing the Cu layer (2 nm) of the device A0 by thefollowing three types of multilayer:

A5: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (1.5 nm)/Cu (0.9 nm)/Ag (0.2 nm)/Cu(0.9 nm)/Co (2 nm)

A6: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (1.5 nm)/Ag (0.2 nm)/Cu (1.8 nm)/Co (2nm)

A7: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (1.5 nm)/Ag (0.2 nm)/Cu (1.8 nm)/Ag(0.2 nm)/Co (2 nm)

Though the MR ratios of these devices A5, A6 and A7 were approximatelythe same as that of the device A0 including the Co layer having athickness of 1.5 nm, the MR sensitivity of these devices was increasedsubstantially twofold. This is presumably because the inserted Ag layerhas a function of weakening the interaction between magnetic layers.Though an Ag layer is herein assumed to be inserted, the presentinvention is effectively applicable in substantially the same way to thecase of inserting an Au layer.

Next, an MR head shown in FIG. 9 was formed by using the device A0 asthe MR device 7 of the present invention and the characteristics of theMR head were evaluated. In this case, the shields 8 and 13 were made ofan Ni₀.8 Fe₀.2 alloy, the insulating layers 9 and 12 were made of Al₂O₃, the hard biasing portion 11 was made of a Co--Pt alloy and the leadportion 10 was formed of Au. In addition, the magnetization directionsof the MR device 7 was adjusted so that the magnetization easy axis ofthe hard magnetic layer is perpendicular to the sheet surface in FIG. 9and the magnetization easy axis of the soft magnetic layer isperpendicular to that of the hard magnetic layer (i.e., a lateraldirection in FIG. 9). Such an adjustment can be achieved by forming thehard magnetic layer while applying a magnetic field using a permanentmagnet to the direction to which an anisotropy was desirably provided.

As a comparative example, an MR head including the comparative MR deviceA1 as described above was fabricated in a similar manner. When theoutputs of these MR heads were measured by applying an AC signalmagnetic field of about 10 Oe to these heads so that the magnetic fieldcoincides with the magnetization direction of the pinned layer (the hardmagnetic layer), the output of the MR head of the present invention wasabout 5 times as high as that of the conventional MR head using anNi--Fe alloy.

EXAMPLE 2

An MR device B0 having the following structure of the type shown in FIG.2 was fabricated by a similar method as that used in the first example:

B0: Co₀.5 Fe₀.5 (3 nm)/Cu (2.5 nm)/Co (1.5 nm)/Co₀.72 Mn₀.08 B₀.2 (2nm)/Co (1.5 nm)/Cu (2.5 nm)/Co₀.5 Fe₀.5 (3 nm)

As a comparative example, a device B1 having the following structureincluding all the layers but the interface magnetic layer 2 shown inFIG. 2 was also fabricated:

B1: Co₀.5 Fe₀.5 (3 nm)/Cu (2.5 nm)/Co₀.72 Mn₀.08 B₀.2 (2 nm)/Cu (2.5nm)/Co₀.5 Fe₀.5 (3 nm)

Furthermore, a device B2 using an Ni--Fe alloy layer as a soft magneticlayer was also modeled:

B2: Co₀.5 Fe₀.5 (3 nm)/Cu (2.5 nm)/Co (1.5 nm)/Ni₀.8 Fe₀.2 (2 nm)/Co(1.5 nm)/Cu (2.5 nm)/Co₀.5 Fe₀.5 (3 nm)

The MR ratios of these devices B0, B1 and B2 were evaluated by a similarmethod as that used in the first example. As a result, the MR ratios ofthese devices B0, B1 and B2 were about 10.1%, about 2.2% and about 3.2%,respectively. In the MR device B0 of the present invention, the softmagnetic characteristics of the soft magnetic layer (or the amorphousalloy layer 1) are excellent and a Co/Cu interface is provided, so thata large MR ratio is realized.

Furthermore, a device B3 in which an interface magnetic layer 2 isinserted into each interface between the hard magnetic layer 4 and thenon-magnetic layer 3 was fabricated by a similar method as thatdescribed above:

B3: Co₀.5 Fe₀.5 (3 nm)/Co (0.5 nm)/Cu (2.5 nm)/Co (1.5 nm)/Co₀.72 Mn₀.08B₀.2 (2 nm)/Co (1.5 nm)/Cu (2.5 nm)/C (0.5 nm)/Co₀.5 Fe₀.5 (2 nm)

The MR ratio of this device B3 was measured by the same method as thatdescribed above. As a result, the MR ratio further increased up to about11.9%. This result tells that the interface magnetic layer 2 has aneffect of increasing the MR ratio even when the interface magnetic layer2 is provided in the interface between the hard magnetic layer 4 and thenon-magnetic layer 3.

Moreover, as a comparative example, a device B4 including a hardmagnetic layer made of a Co₀.2 Fe₀.8 alloy was fabricated by a similarmethod as that used for fabricating the device B0:

B4: Co₀.2 Fe₀.8 (3 nm)/Cu (2.5 nm)/Co (1.5 nm)/Co₀.72 Mn₀.08 B₀.2 (2nm)/Co (1.5 nm)/Cu (2.5 nm)/Co₀.2 Fe₀.8 (3 nm)

The MR ratio of this device B4 was about 4.3%, which was considerablylower than that of the device B0. Moreover, the square ratios of thehard magnetic layers of the devices B4 and B0 were measured based on themagnetization curves. As a result, the square ratio of the device B4 wasabout 0.6, whereas that of the device B0 of the present invention wasabout 0.87. That is to say, as seen from this example, the square ratioof a hard magnetic layer is required to be 0.7 or more.

EXAMPLE 3

An MR device C0 having the following structure of the type shown in FIG.3 using an antiferromagnetic layer was fabricated by a similar method asthat used in the first example:

C0: Co₀.68 Mn₀.06 B₀.26 (3 nm)/Co (1.5 nm)/Cu (2 nm)/Ni₀.8 Fe₀.2 (3nm)/Ni₀.44 Mn₀.56 (10 nm)

As a comparative example, an MR device C1 having the following structureusing an Ni--Fe alloy layer as a soft magnetic layer was also modeled:

C1: Ni₀.8 Fe₀.2 (3 nm)/Co (1.5 nm)/Cu (2 nm)/Ni₀.8 Fe₀.2 (3 nm)/Ni₀.44Mn₀.56 (10 nm)

The characteristics of these MR devices C0 and C1 were evaluated by asimilar method as that used in the first example. As a result, the MRratios of these two devices were substantially equal to each other.However, comparing the slopes of the MR curves (i.e., the values of theMR sensitivity ΔMR/ΔH), the device C0 has a slope approximately twice assteep as that of the device C1. This is presumably because the device C0using an amorphous alloy and a Co layer as a soft magnetic layer hasmore satisfactory soft magnetic characteristics.

In this example, a Co layer is assumed to be used as an interfacemagnetic layer. However, even when Co₀.9 Fe₀.1 was used for theinterface magnetic layer, substantially the same result was obtained.Also, in this example, an Ni--Mn alloy was used for a metalantiferromagnetic layer 6. Alternatively, the present invention iseffectively applicable to the cases of using an Ir--Mn alloy, a Pd--mnalloy, a Pt--Mn alloy, a Fe--Ir alloy and the like.

Next, an MR head shown in FIG. 9 was formed by using the device C0 asthe MR device 7 of the present invention and the characteristics of theMR head were evaluated. In this case, the shields 8 and 13 were made ofan Ni₀.8 Fe₀.2 alloy, the insulating layers 9 and 12 were made of Al₂O₃, the hard biasing portion 11 was made of a Co--Pt alloy and the leadportion 10 was made of Au. In addition, an anisotropy was provided suchthat the magnetization easy axis of the magnetic layer 5 and that of thesoft magnetic layer respectively became parallel and vertical to themagnetic field direction corresponding to the signal to be detected. Inthis method, when the magnetic layer was deposited, a magnetic field wasapplied by a permanent magnet to the direction within the layer to whichan anisotropy was desirably applied.

As a comparative example, an MR head was fabricated in a similar mannerexcept that an Ni₀.8 Fe₀.2 alloy was used for the MR device 7. When theoutputs of these MR heads were measured by applying an AC signalmagnetic field of about 10 Oe to these heads, the output of the MR headof the present invention was about 4 times as high as that of aconventional MR head.

EXAMPLE 4

An MR device D0 having the following structure of the type shown in FIG.4, which includes a combination of an antiferromagnetic layer and amagnetic layer in place of a hard magnetic layer, was fabricated by asimilar method as that used in the third example:

D0: Ta (10 nm)/Ni₀.44 Mn₀.56 (10 nm)/Ni₀.8 Fe₀.2 (2 nm)/Cu (2 nm)/Co (1nm)/Co₀.68 Mn₀.26 B₀.26 (3 nm)/Co (1 nm)/Cu (2 nm)/Ni₀.8 Fe₀.2 (2nm)/Ni₀.44 Mn₀.56 (10 nm)

As a comparative example, an MR device D1 of the type without interfacemagnetic layers 2 was also modeled:

D1: Ta (10 nm)/Ni₀.44 Mn₀.56 (10 nm)/Ni₀.8 Fe₀.2 (2 nm)/Cu(2 nm)/Co₀.68Mn₀.06 B₀.26 (3 nm)/Cu (2 nm)/Ni₀.8 Fe₀.2 (2 nm)/Ni₀.44 Mn₀.56 (10 nm)

The characteristics of these MR devices D0 and D1 were evaluated by thesame method as that used in the first example. As a result, the MR ratioof the MR device D0 was about 9.5%, whereas the MR ratio of the deviceD1 was about 2.6%. The ΔMR/ΔH value of the device D0 was approximatelyfour times as high as that of the device D1. This result also proves theeffects attained by the interface magnetic layers.

EXAMPLE 5

An MR device E0 having a structure shown in FIG. 5 was fabricated on asubstrate (for example, a glass substrate) by an RF magnetron sputteringapparatus with six targets. The specific structure of the MR device E0is as follows:

E0: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Cu (2 nm)/Co₀.68 Mn₀.06 B₀.26 (2nm)/Ir₀.2 Mn₀.8 (10 nm)

where the numerical values in parentheses indicate layer thicknesses.

A comparative MR device E1 having the following structure including softmagnetic layers made of an Ni--Fe alloy was fabricated by a similarmethod.

E1: Ni₀.8 Fe₀.2 (2 nm)/Cu (2 nm)/Ni₀.8 Fe₀.2 (2 nm)/Ir₀.2 Mn₀.8 (10 nm)

The following Table 1 shows the results of the characteristics of the MRdevices E0 and E1 fabricated in such a manner which were evaluated by adirect current four-terminal method in which an external magnetic fieldof about 500 Oe was applied at room temperature.

                  TABLE 1                                                         ______________________________________                                        Sample Name  MR ratio (%)                                                                             ΔMR/ΔH (% kA/m)                           ______________________________________                                        E0           3.1        1                                                     E1           1.9        0.3                                                   ______________________________________                                    

As seen from Table 1, the MR device E0 of the present invention has alarger MR ratio and a higher MR sensitivity ΔMR/ΔH than those of thecomparative MR device E1. The reason is probably as follows: because theMR device E0 uses an amorphous alloy having excellent soft magneticcharacteristics for a soft magnetic layer, the MR sensitivity of thedevice E0 has been improved.

Next, an MR head shown in FIG. 9 was formed by using the device E0 ofthe present invention as the MR device 7 and the characteristics of theMR head were evaluated. In this case, the shields 8 and 13 were made ofan Ni₀.8 Fe₀.2 alloy, the insulating layers 9 and 12 were made of Al₂O₃, the hard biasing portion 11 was made of a Co--Pt alloy and the leadportion 10 was made of Au. In addition, an anisotropy was provided suchthat the magnetization easy axis of one of the amorphous alloy layers 1in contact with the metal antiferromagnetic layer 6 and themagnetization easy axis of the other amorphous alloy layer 1 functioningas a free layer respectively became parallel and vertical to themagnetic field direction corresponding to the signal to be detected. Inthis method, when the metal antiferromagnetic layer and the softmagnetic layer contacting the metal antiferromagnetic layer weredeposited, a magnetic field was applied by a permanent magnet to thedirection within the layer to which an anisotropy was desirably applied.

As a comparative example, an MR head was fabricated in a similar mannerexcept that the comparative MR device E1 including an Ni₀.8 Fe₀.2 alloywas used for the MR device 7. When the outputs of these MR heads weremeasured by applying an AC signal magnetic field of about 10 Oe to theseheads, the output of the MR head using the MR device E0 of the presentinvention was about 3 times as high as that of a conventional MR headusing the comparative MR head E1.

In this example, a Co--Mn--B layer is assumed to be used as an amorphousalloy layer. However, the corrosion resistance of a Co--Mn--B layer anda Co--Fe--B layer is slightly deteriorated under extremely badconditions, (e.g., in water or in saline water). In order to eliminatesuch a disadvantage, a Co--Nb--Zr layer may be used. When an MR deviceE2 having the following structure was modeled in a similar manner exceptfor using Co₀.85 Nb₀.1 Zr₀.05 as a target,

E2: Co₀.85 Nb₀.05 Zr₀.05 (2 nm)/Cu (2 nm)/Co₀.85 Nb₀.1 Zr₀.05 (2nm)/Ir₀.2 Mn₀.8 (10 nm)

the MR device E2 exhibited excellent characteristics: the MR ratiothereof was about 2.9% and the MR sensitivity ΔMR/ΔH was 0.8%.

Furthermore, in order to examine the characteristics of the non-magneticlayer, the following three types of devices E3, E4 and E5 werefabricated by replacing the Cu layer (2 nm) by the following three typesof multilayer.

E3: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Cu (0.9 nm)/Ag (0.2 nm)/Cu (0.9nm)/Co₀.68 Mn₀.06 B₀.26 (2 nm)/Ir₀.2 Mn₀.8 (10 nm)

E4: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Ag (0.2 nm)/Cu (1.8 nm)/Co₀.68 Mn₀.06B₀.26 (2 nm)/Ir₀.2 Mn₀.8 (10 nm)

E5: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Cu (1.8 nm)/Ag (0.2 nm)/Co₀.68 Mn₀.06B₀.26 (2 nm)/Ir₀.2 Mn₀.8 (10 nm)

These MR devices E3, E4 and E5 were evaluated in a similar manner tothat described in the first example. Though the MR ratios of these MRdevices E3, E4 and E5 were approximately the same as that of the deviceE0, the MR sensitivity of these devices was increased by a factorsubstantially equal to 1.5. This is presumably because the inserted Aglayer has a function of weakening the interaction between magneticlayers. Though an Ag layer is herein assumed to be inserted, the presentinvention is effectively applicable in substantially the same way to thecase of inserting an Au layer.

Also, in this example, an Ir--Mn alloy was used for the metalantiferromagnetic layer 6. Alternatively, the present invention isapplicable to the cases of using a Pt--Mn alloy, a Pd--mn alloy, aNi--Mn alloy, a Fe--Ir alloy and the like.

EXAMPLE 6

An MR device F0 having a structure shown in FIG. 7 was fabricated on asubstrate (for example, a glass substrate) by a similar method as thatused in the fifth example. The specific structure of the MR device F0 isas follows:

F0: Ir₀.2 Mn₀.8 (10 nm)/Co₀.68 Mn₀.06 B₀.26 (2 nm)/Cu (2 nm)/Co₀.68Mn₀.06 B₀.26 (2 nm)/Cu (2 nm)/Co₀.68 Mn₀.06 B₀.26 (2 nm)/Ir₀.2 Mn₀.8 (10nm)

As a comparative conventional example, an MR device F1 having thefollowing structure in which the Co₀.68 Mn₀.06 B₀.26 layer as theamorphous alloy layer is replaced by an Ni₀.8 Fe₀.2 layer was alsomodeled:

F1: Ir₀.2 Mn₀.8 (10 nm)/Ni₀.8 Fe₀.2 (2 nm)/Cu (2 nm)/Ni₀.8 Fe₀.2 (2nm)/Cu (2 nm)/Ni₀.8 Fe₀.2 (2 nm)/Ir₀.2 Mn₀.8 (10 nm)

The following Table 2 shows the results of the characteristics of thedevices F0 and F1 fabricated in such a manner which were evaluated bythe same method as that used in the fifth example.

                  TABLE 2                                                         ______________________________________                                        Sample Name  MR ratio (%)                                                                             ΔMR/ΔH (% kA/m)                           ______________________________________                                        F0           5.2        1.7                                                   F1           3.6        0.5                                                   ______________________________________                                    

As seen from Table 2, the MR device F0 of the present invention has alarger MR ratio and a higher MR sensitivity ΔMR/ΔH than those of thecomparative MR device F1. The reason is probably as follows: because theMR device F0 uses an amorphous alloy having excellent soft magneticcharacteristics for a soft magnetic layer, the MR sensitivity of the MRdevice F0 has been improved.

Next, an MR head shown in FIG. 9 was formed by using the MR device F0 ofthe present invention as the MR device 7 and the characteristics of theMR head were evaluated in the same way as in the first example. Inaddition, for comparison, an MR head having a structure shown in FIG. 9which includes the comparative MR device F1 was fabricated in a similarmanner. This MR head was evaluated in a similar manner to that used inthe first example. As a result, the output of the MR head of the presentinvention was about twice as high as that of the MR head using thecomparative MR device F1.

EXAMPLE 7

An MR device G0 having a structure shown in FIG. 6A was fabricated on asubstrate, such as a glass substrate, by an RF magnetron sputteringapparatus using a ternary target. The specific structure of the MRdevice G0 is as follows:

G0: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (t nm)/Cu (2 nm)/Co (t nm)/Co₀.68Mn₀.06 B₀.26 (2 nm)/Ir₀.2 Mn₀.8 (10 nm)

where the numerical values in parentheses indicate layer thicknesses. Inthis MR device G0, the layer thickness t of the Co layers was varied tobe selected from the range of about 0 to about. 3 nm.

The following Table 3 shows the results of the characteristics of thedevice G0 fabricated in such a manner which were evaluated by a directcurrent four-terminal method in which an external magnetic field ofabout 500 Oe was applied at room temperature.

                  TABLE 3                                                         ______________________________________                                        Thickness of              ΔMR/ΔH                                  Co layer (nm)  MR ratio (%)                                                                             (% kA/m)                                            ______________________________________                                        0              3.1        1                                                   0.2            4.3        1.3                                                 0.5            5.2        1.4                                                 1              6.2        1.9                                                 1.5            6.0        1.8                                                 2              6.3        2.1                                                 2.5            4.8        1.0                                                 3              4.5        0.7                                                 ______________________________________                                    

As is clear from Table 3, both the MR ratio and the MR sensitivityΔMR/ΔH are considerably improved by the insertion of the Co layersbetween the non-magnetic layer 3 and the amorphous alloy layers 1. Thismeans that the magnetic scattering occurring at the interface of the Colayer as the interface magnetic layer and the Cu layer as thenon-magnetic layer is larger than that occurring at the interface of theCo₀.68 Mn₀.06 B₀.26 layer as the amorphous alloy layer and the Cu layer.

As is apparent from Table 3, though some effects can be attained whenthe thickness of the Co layer to be inserted is set to be about 0.2 nm,the thickness of the Co layer is preferably about 1 nm or more. However,when the thickness of the Co layer is about 2.5 nm or more, both the MRratio and the MR sensitivity ΔMR/ΔH are decreased. This is presumablybecause the soft magnetic characteristics of the soft magnetic layersare deteriorated when the Co layer is too thick. As shown in Tables 1and 3, when the thickness of the Co layer is about 2 nm or less, boththe MR ratio and the MR sensitivity ΔMR/ΔH of the MR device G0 of thepresent invention are much improved as compared with the comparative MRdevice E1 described in the fifth example.

In this example, the interface magnetic layers are assumed to beinserted into both sides of the non-magnetic layer 3 as shown in FIG.6A. Alternatively, increase of the MR ratio and improvement of the MRsensitivity ΔMR/ΔH can be attained in the cases of inserting a singleinterface magnetic layer to either one side of the non-magnetic layer 3as shown in FIGS. 6B and 6C. The MR devices G2 and G3 respectivelyhaving structures shown in FIGS. 6B and 6C were fabricated on asubstrate by a similar method to the fabrication method of the MR deviceF0. The specific structure of the MR devices G2 and G3 were as follows:

G2: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Cu (2 nm)/Co (t nm)/Co₀.68 Mn₀.06 B₀.26(2 nm)/Ir₀.2 Mn₀.8 (10 nm)

G3: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (t nm)/Cu (2 nm)/Co₀.68 Mn₀.06 B₀.26(2 nm)/Ir₀.2 Mn₀.8 (10 nm)

These MR devices G2 and G3 were evaluated in a similar method that usedin the first example. The evaluation results are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Sample Name  MR ratio (%)                                                                             ΔMR/ΔH (% kA/m)                           ______________________________________                                        G2           4.8        1.5                                                   G3           4.2        1.3                                                   ______________________________________                                    

As is clear from the results shown in Table 4, even when an interfacemagnetic layer is inserted to either one side of a non-magnetic layer,the MR characteristics of the device are still superior to those of thedevice D1 including no interface magnetic layer described in the fourthexample.

In this example, a Co layer is assumed to be used as an interfacemagnetic layer. However, substantially the same effects were attainedeven when Co₀.9 Fe₀.1 was used for the interface magnetic layer.

Also, in this example, an amorphous alloy layer is assumed to be indirect contact with an antiferromagnetic layer. Alternatively, acrystalline magnetic layer may be inserted between the amorphous alloylayer and the metal antiferromagnetic layer. For comparison, an MRdevice G0 in which the thickness of the Co layer was 1 nm and an MRdevice G4 having a Ni--Fe--Co layer as the crystalline magnetic layerbetween the amorphous alloy layer and the metal antiferromagnetic layerwere fabricated as follows:

G0: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (1 nm)/Cu (2 nm)/Co (1 nm)/Co₀.68Mn₀.06 B₀.26 (2 nm)/Ir₀.2 Mn₀.8 (10 nm)

G4: Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (t nm)/Cu (2 nm)/Co (t nm)/Co₀.68Mn₀.06 B₀.26 (2 nm)/Ni₀.8 Fe₀.1 Co₀.1 (1.5 nm)/Ir₀.2 Mn₀.8 (10 nm)

These MR devices G0 and G4 were evaluated by a similar method to thatused in the first example. The device G4 had an MR ratio and an MRsensitivity ΔMR/ΔH substantially equal to those of the device G0, andthe magnetic field required for inverting the magnetic domain in thepinned layer of the device G4 was about 200 Oe, i.e., about twice ofthat (about 100 Oe) of the device G0. Consequently, the MR device G4 canbe practically used as a member of a magnetic head.

EXAMPLE 8

An MR device H0 having a structure shown in FIG. 8 was fabricated by asimilar method to that used in the fifth example. The specific structureof the MR device H0 was as follows:

H0: Ir₀.2 Mn₀.8 (10 nm)/Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (1 nm)/Cu (2nm)/Co (1 nm)/Co₀.68 Mn₀.06 B₀.26 (2 nm)/Co (1 nm)/Cu (2 nm)/Co (1nm)/Co₀.68 Mn₀.06 B₀.26 (2 nm)/Ir₀.2 Mn₀.8 (10 nm)

A comparative MR device H1 having the following structure was similarlyfabricated.

H1: Ir₀.2 Mn₀.8 (10 nm)/Ni₀.8 Fe₀.2 (2 nm)/Co (1 nm)/Cu (2 nm)/Co (1nm)/Ni₀.8 Fe₀.2 (2 nm)/Co (1 nm)/Cu (2 nm)/Co (1 nm)/Ni₀.8 Fe₀.2 (2nm)/Ir₀.2 Mn₀.8 (10 nm)

The following Table 5 shows the evaluation results of thecharacteristics of the devices H0 and H1 fabricated in such a mannerwhich were evaluated by the same method as that used in the fifthexample.

                  TABLE 5                                                         ______________________________________                                        Sample Name  MR ratio (%)                                                                             ΔMR/ΔH (% kA/m)                           ______________________________________                                        H0           6.9        2.3                                                   H1           3.3        0.4                                                   ______________________________________                                    

As seen from Table 5, the MR device H0 of the present invention has alarger MR ratio and a higher MR sensitivity ΔMR/ΔH than those of thecomparative MR device H1. The reason is probably as follows: because theMR device H0 uses an amorphous alloy having excellent soft magneticcharacteristics for a soft magnetic layer, the MR sensitivity of the MRdevice H0 has been improved.

Next, an MR head shown in FIG. 9 was formed by using the MR device H0 ofthe present invention as the MR device 7 in a similar way to thatdescribed in the fifth example and the characteristics of the MR headwere evaluated. In addition, an MR head having a structure shown in FIG.9 which includes the comparative MR device H1 was also fabricated andevaluated. As a result, the output of the MR head of the presentinvention was about 7 times as high as that of a conventional MR headusing the comparative MR device H1 including Ni--Fe alloy layers.

The foregoing examples have been described mainly about the cases wherea Co--Mn--B alloy is used for an amorphous alloy layer. However, thepresent inventors confirmed that the same effects were also attained inthe cases of using a Co(--Fe, Mn)--Nb--B alloy, a Co--Nb--Zr alloy andthe like.

As is apparent from the foregoing description, the MR device of thepresent invention realizes a large MR change in a low magnetic field.Thus, if the MR device of the present invention is applied to a magnetichead, the reproduced output thereof can be considerably increased in avery weak magnetic field. In addition, since the total thickness of theMR device of the present invention can be relatively small, the MRdevice of the present invention will be effectively applicable to amagnetic head for super high-density recording to be developed in thenear future.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A magnetoresistive device comprising:a softmagnetic layer; at least one hard magnetic layer; at least onenon-magnetic layer formed between the soft magnetic layer and the atleast one hard magnetic layer, the non-magnetic layer having a thicknessof at least about 1.5 nm; and an interface magnetic layer, provided atan interface between the soft magnetic layer and the at least onenon-magnetic layer, for enhancing a spin-dependent scattering ofconduction electrons at the interface between the non-magnetic layer andthe soft magnetic layer, and improving soft magnetic properties of thesoft magnetic layer, the interface magnetic layer having a thickness ofat least 0.2 nm,wherein the soft magnetic layer includes an amorphousstructure, and an axis of easy magnetization of the hard magnetic layersubstantially coincides with a direction of a magnetic field to bedetected.
 2. A magnetoresistive device according to claim 1, wherein theinterface magnetic layer mainly contains Co or Co--Fe alloy, and have athickness of about 2 nm or less.
 3. A magnetoresistive device accordingto claim 1, wherein the hard magnetic layer has a ratio of remanentmagnetization to saturation magnetization is about 0.7 or more.
 4. Amagnetoresistive device according to claim 1, wherein the hard magneticlayer is partially or entirely formed of oxide.
 5. A magnetoresistivedevice according to claim 4, wherein the hard magnetic layer is formedof an oxide of Co or an oxide of Fe.
 6. A magnetoresistive deviceaccording to claim 1, wherein the hard magnetic layer contains Co_(x)Fe_(1-x) as a main component, where x is in a range of about 0.3 toabout 0.7.
 7. A magnetoresistive device according to claim 1, furthercomprising an oxide layer formed on a side of the hard magnetic layeropposite to a side on which the non-magnetic layer is formed.
 8. Amagnetoresistive device according to claim 7, wherein the oxide layer isformed of an oxide of Ni.
 9. A magnetoresistive device according toclaim 1, further comprising an oxide magnetic layer formed on a side ofthe hard magnetic layer opposite to a side on which the non-magneticlayer is formed.
 10. A magnetoresistive device according to claim 9,wherein the oxide magnetic layer is formed of an oxide of Co or an oxideof Fe.
 11. A magnetoresistive device according to claim 6, furthercomprising an oxide magnetic layer formed on a side of the hard magneticlayer opposite to a side on which the non-magnetic layer is formed. 12.A magnetoresistive device according to claim 11, wherein the oxidemagnetic layer is formed of an oxide of Co or an oxide of Fe.
 13. Amagnetoresistive device according to claim 1, wherein the non-magneticlayer includes a non-magnetic layer of a different material insertedtherein.
 14. A magnetoresistive device according to claim 13, whereinthe non-magnetic layer of the different material has a thickness ofabout 1 nm or less.
 15. A magnetoresistive device according to claim 1,further comprising a further interface magnetic layer provided at aninterface between the hard magnetic layer and the non-magnetic layer.16. A magnetoresistive device according to claim 15, wherein the furtherinterface magnetic layer mainly contains Co or Co--Fe alloy and has athickness of about 2 nm or less.
 17. A magnetoresistive device accordingto claim 1, wherein the soft magnetic layer mainly contains Co--Mn--Balloy.
 18. A magnetoresistive device according to claim 1, wherein thesoft magnetic layer mainly contains Co--Nb--Zr alloy.
 19. Amagnetoresistive device according to claim 1, wherein the soft magneticlayer mainly contains Co--Nb--B alloy.
 20. A magnetoresistive deviceaccording to claim 1, wherein the magnetoresistive device has athickness of about 20 nm or less, but greater than zero.
 21. Amagnetoresistive head comprising an magnetoresistive device according toclaim 20, and a lead portion.
 22. A magnetoresistive device according toclaim 1, wherein the non-magnetic layer has a thickness of about 10 nmor less but at least about 1.5 nm.
 23. A magnetoresistive deviceaccording to claim 1, wherein the non-magnetic layer has a thickness ofabout 10 nm or less but at least about 1.8 nm.
 24. A magnetoresistivedevice according to claim 1, wherein the non-magnetic layer has athickness of about 3 nm or less but at least about 1.5 nm.
 25. Amagnetoresistive device according to claim 1, wherein the non-magneticlayer has a thickness of about 3 nm or less but at least about 1.8 nm.26. A magnetoresistive device according to claim 1, wherein theinterface layer has a thickness of about 2 nm or less but at least 0.2nm.
 27. A magnetoresistive device according to claim 1, wherein theinterface layer has a thickness of about 2 nm or less but at least 0.8nm.
 28. A magnetoresistive device according to claim 1, wherein theinterface layer has a thickness of about 1.8 nm or less but at least 0.2nm.
 29. A magnetoresistive device according to claim 1, wherein theinterface layer has a thickness of about 1.8 nm or less but at least 0.8nm.
 30. A magnetoresistive device according to claim 1, wherein the softmagnetic layer including an amorphous structure has a thickness of 10 nmor less.
 31. A magnetoresistive device according to claim 1, wherein thesoft magnetic layer including an amorphous structure has a thickness of5 nm or less.
 32. A magnetoresistive device comprising:a soft magneticlayer; at least one hard magnetic layer; at least one non-magnetic layerformed between the soft magnetic layer and the at least one hardmagnetic layer, the non-magnetic layer having a thickness of about 10 nmor less but at least about 1.5 nm; and an interface magnetic layer,provided at an interface between the soft magnetic layer and the atleast one non-magnetic layer, for enhancing a spin-dependent scatteringof conduction electrons at the interface between the non-magnetic layerand the soft magnetic layer, and improving soft magnetic properties ofthe soft magnetic layer, the interface magnetic layer having a thicknessof about 2 nm or less but at least 0.2 nm,wherein the soft magneticlayer includes an amorphous structure and has a thickness of 10 nm orless, and an axis of easy magnetization of the hard magnetic layersubstantially coincides with a direction of a magnetic field to bedetected.
 33. A magnetoresistive device comprising:a soft magneticlayer; at least one hard magnetic layer; at least one non-magnetic layerformed between the soft magnetic layer and the at least one hardmagnetic layer, the non-magnetic layer having a thickness of about 10 nmor less but at least about 1.5 nm; and an interface magnetic layer,provide at an interface between the soft magnetic layer and the at leastone non-magnetic layer, for enhancing a spin-dependent scattering ofconduction electrons at the interface between the non-magnetic layer andthe soft magnetic layer, and improving soft magnetic properties of thesoft magnetic layer, the interface magnetic layer having a thickness ofabout 2 nm or less but at least 0.2 nm,wherein the soft magnetic layerincludes an amorphous structure and has a thickness of 10 nm or less butgreater than zero, the magnetoresistive device has a thickness of about20 nm or less but greater than zero, and an axis of easy magnetizationof the hard magnetic layer substantially coincides with a direction of amagnetic field to be detected.